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Ventless Dryers and Laundry Room Exhaust Fans

hambone8780 | Posted in Building Code Questions on

Howdy! Matt Risinger recently did an episode on ventless dryers in a tight build. He did some musing on the lost conditioned air when a vented dryer is running, but didn’t have numbers. That led me to this article:, which was a very interesting read.

I’m considering going to a ventless dryer for our cabin build, which I’m familiar with in our primary home. I’m curious if anyone has done the calculations for energy saved by not exhausting conditioned air via the dryer.

Also, are there code requirements for an exhaust fan in a laundry room (2015 code – Marine-4 Climate Zone)? My thinking is that I can save some time and energy (literally) by not installing a dryer exhaust or laundry room/closet exhaust fan.

Thanks for all the great information!

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  1. DennisWood | | #1

    Assuming 200 CFM that a typical dryer exhausts, outside temp of 32 F, and inside temp of 70 F, you would need 2405 watts to heat the replacement air. Assuming a 45 minute average cycle time, you'd be at about 1.8 kWh to heat make up air. The relative efficiency is quite a bit more than you'd think just comparing the appliance power use, particularly if you use the dryer a lot.

    We've been using a heat pump dryer (full size Whirlpool, unlike the smaller ones Matt is using) for about six years now. There have been no issues, other than requiring cleaning the evaporator and condenser units (pulled the case, about 2 hours) recently.

    1. hambone8780 | | #2

      Thanks! We've had one for a while now too, and the systems are great!

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